Mucinex is an expectorant medication used for the temporary relief of coughs caused by the common cold, bronchitis, and other breathing illnesses. It works by thinning and loosening mucus in the airways, clearing congestion, and making breathing easier. Mucinex is usually not used for ongoing cough from smoking or long-term breathing problems (such as chronic bronchitis, emphysema) unless directed by a doctor. Mucinex products should be used exactly as directed on the label or as prescribed by a doctor, and it is important to follow all dosage directions to decrease the risk of serious side effects. Mucinex products should not be used to make a child sleepy, and other cough-and-cold medication that might contain the same or similar ingredients should not be given. If you are self-treating with Mucinex, it is important to read the package instructions carefully before use to be sure it is right for you.